Tetractinellida \Te*trac`ti*nel"li*da\, n. pl. [NL., from Gr. te`tra- tetra- + ?, ?, ray, spoke.] (Zo["o]l.) A division of Spongi[ae] in which the spicules are siliceous and have four branches diverging at right angles. Called also {Tetractinellin[ae]}.